Third-generation (3G) wireless networks, such as International Mobile Telecommunications 2000 (IMT-2000), third generation partnership project (3GPP), third generation partnership project 2 (3GPP2), and so forth, aim to provide multimedia mobile services having bit rates with a goal of between about 6 and 54 Mbps and higher. As the deployment of 3G networks continues in different regions of the world, researchers have already begun proposing how 3G networks may evolve to beyond 3G or fourth-generation (4G) networks attempting to reach bit rates of 100 Mbps and above. To achieve a successful and profitable commercial market for 3G, and beyond, network service designers and providers are paying attention to efficient utilization of radio resources. Although the available bandwidth is much larger in 3G, and beyond, networks (compared to second-generation [2G] networks), it is still important to efficiently utilize radio resources due to continued growth of the wireless subscriber population, increasing demand for new mobile multimedia services over wireless networks, and more stringent quality of service (QoS) requirements in terms of transmission accuracy, delay, jitter, throughput, and the like.
The capacity of single-antenna communications systems may likely be insufficient to meet the expected demands for higher data rates, lower delays, and higher overall quality of future networks. Multiple antenna configurations offer an opportunity to transmit to and receive from multiple users simultaneously with much higher data rates than single-antenna communications systems. Multiple Input, Multiple Output (MIMO) technologies and Orthogonal Frequency Division Multiple Access (OFDMA) have been identified by the major standards bodies, such as 3G Partnership Project (3GPP), 3GPP2, WiMAX Forum, and the like, as potential methodologies for implementing the physical layer of the next generation wireless networks. Multi-antenna, multi-user communications systems using MIMO and OFDMA technologies provide a rich environment for satisfying the needs of new networks and new services. Space Division Multiple Access (SDMA), in both the downlink (DL) and uplink (UL) transmissions of such communications systems, is also of special interest because it facilitates multiplexing of the multiple users over the same time-frequency resource blocks with no change in hardware, since a single transmit antenna at the access terminal (AT) is sufficient. Furthermore, user coordination is not generally required because the base station (BS) typically makes all of the decisions. The spatial signatures at the base station antenna array are different for each user and, therefore, may be used to distinguish the signals transmitted on the same time-frequency resource blocks.
FIG. 1 illustrates a diagram of a portion of a wireless communications system 100. As shown in FIG. 1, an antenna 105, such as an antenna of a BS 110 operating in the wireless communications system 100, may be partitioned into three sectors, such as sector 115 and sector 116. Although shown in FIG. 1 as a single antenna, the antenna 105 may be comprised of three individual antennas, with one antenna per sector. The BS 110 may be capable of transmitting separate signals within the different sectors. Furthermore, the BS 110 may spatially divide the signals to multiple mobile stations (MS), such as MS 120 and MS 121, within their respective sectors. Alternate names for a MS may be user, mobile terminal (MT), user equipment (UE), access terminal (AT), and so forth. In general, these names may be used interchangeably.
For SDMA-based multi-user MIMO communications systems, the receivers may use various interference canceling methodologies, such as Dirty Paper Coding (DPC), which generally pre-cancels known interferences at the base station, and other successive interference cancellation techniques. These technologies and techniques have been suggested as the optimal solutions for the DL and UL, respectively. However, SDMA transmission performance is still largely dependent on the correlation among the spatial signatures, and performance advantage is typically only present when users are carefully selected or grouped for DL or UL transmissions. Therefore, the scheduling scheme (sometimes referred to as user grouping) becomes very important in SDMA communications systems.
There have been simple scheduling algorithms proposed for selecting users for grouping in an UL of an SDMA-based multi-user MIMO communications system. However, most existing SDMA scheduling algorithms are based on an exhaustive, optimization selection search for which the computational complexity grows exponentially as the number of users increase. This may become computationally intensive when the communications system is heavily loaded. Furthermore, these algorithms, both simple and complex, are typically selected to maximize throughput without consideration of other constraints, such as QoS constraints, fairness, and so forth.
In addition to the algorithms for selecting the users to be scheduled, the optimal transmission power for each scheduled user is also determined by the BS for both the DL and UL transmissions. In DL transmission, the BS is allocating the BS's power for transmission to the multiple mobile stations (MS) that have been scheduled. In the UL, the BS allocates the division of power for the multiple MS. As with most of the other existing methodologies, power allocation has generally focused on maximizing the total throughput, again, with no consideration of other constraints, such as the QoS constraints, fairness, and so forth. Different types of media may have different constraints. For example, real-time applications, such as voice over internet protocol (VoIP) and videoconferencing, are delay-sensitive, while data applications can tolerate a certain degree of delay and throughput is a higher concern. Therefore, with advanced 3G, 4G, and beyond, networks aiming to provide true multimedia traffic, the typical throughput-centric scheduling algorithms currently being used may become increasingly insufficient to adequately support truly advanced networks.